A major British institutional investor will tomorrow oppose the re-election of Lee Raymond as chief executive of ExxonMobil on "ethical grounds" at its annual meeting.

The challenge will be launched by the Co-operative Insurance Society (CIS) which says the world's biggest stock-listed oil company talks down links between man-made CO2 emissions and climate change. Exxon, under Mr Raymond's leadership, has lobbied against the Kyoto protocol on greenhouse gases and against the US government signing the treaty, the CIS believes.

The investor, which holds $25m worth of Exxon stock, is also opposed to Mr Raymond's double role as chairman and chief executive of the company which trades in the UK under the Esso banner. "We are taking this unprecedented action of opposing the election of a chief executive as we have serious concerns on their management of climate change and the leadership provided on this issue," said Ian Jones, head of responsible investment at CIS.

The corporate reputation of Exxon is being damaged by the "head in the sand" approach of Mr Raymond in the face of evidence that human activity is a significant contributor to climate change and extreme weather, argues the CIS.

"In the long term, their reluctance to invest in renewables generation now indicates an aversion to managing this gravest of all environmental issues," it added.

And it claims to be better-placed than many to comment on this issue because it has witnessed the rising insurance claims coming through due to global warming. Environmental flooding alone has led to a 500% increase in claims over the past decade which now total more than £1.5m a year, the CIS says.

Exxon, which also faces a Stop Esso petrol campaign from environmentalists, has always said that its critics misunderstood its position.

"We recognise that the risk of climate change and its potential impacts on society and ecosys tems may prove to be significant, and these are issues we take seriously," an Exxon spokesman said last night.

"While studies must continue to better understand these risks and possible consequences, we will continue to take actions and work with others on ways to bring scientific and technological expertise to energy-related solutions that are technically and economically viable," it added.